Various forms of football have been played over the years, the tame ones played with pigs bladders and the wild ones with human heads.
The oldest form of Football is Gaelic football which was played by warriors.
Although I believe that Terry Pratchett was just getting at the extremities of Football fans and what they do when they often dont even watch the game. And of course comically exaggerating this.
Any one who is interested in this should watch the film Football Factory.
And Welcome to the site:)